The invention relates generally to alternating current and direct current electric motors. More specifically, the invention is directed to an electric motor having improved efficiency.
Conventional electric motors include a stator and a rotor which cooperate to produce a torque on the rotor shaft when current is induced in the rotor windings. Torque is created when current is induced in the rotor windings since the rotor windings establish a plurality of magnetic north and south poles on the rotor which are attracted and repelled by south and north pole sections of the stator, respectively. In most cases, rotors are provided with distributed windings which are spread over a number of slots disposed about the periphery of the rotor. With distributive windings, the individual coils of the windings are interconnected to provide belts of conductors in the slots carrying oppositely directed currents parallel to the shaft and arranged to produce the same number of poles as the stator. In general, conventional electric motor designs provide stator and rotor magnetic poles of uniform and equal magnitude. As a result, in conventional electric motor designs, there are often particular angular orientations of the rotor where the rotor poles are not optimally disposed to create the greatest torque.
It is known that the shape of the core of an electromagnet, such as those used to establish the stator field of an electric motor, may be altered to generate a magnetic field gradient. The prior art also reveals examples of electric motors having current limiting devices, such as resistors, connected in series with rotor windings for the purpose of controlling speed, acceleration, and the load on an electric motor. Various devices for energizing or controlling a predetermined sequence of armature windings are also revealed in the prior art. However, the prior art has not considered the combination of these features in an effort to provide an electric motor having an improved disposition of attracting and repelling forces and thus an improved efficiency.